A shock absorber is used in vehicles, devices, structures and the like. Generally, such a shock absorber includes a cylinder in which working fluid is sealed, a piston in sliding contact with the inner peripheral surface of the cylinder to partition the interior of the cylinder into two chambers, a piston rod having one end part coupled to the piston and the other end side extending outwardly of the cylinder, a flow passage allowing communication between the two chambers and damping force generation means for applying resistance to the working fluid passing in the flow passage.
For example, in a shock absorber used as the one for vehicle, a cylinder is coupled to one of a vehicle body side as a vibration damping target and a wheel side as a vibration input part and a piston rod is coupled to the other of the vehicle body side and the wheel side. In such a shock absorber, a piston moves in the cylinder by the input of vibration and the working fluid in one chamber pressurized by the piston moves to the other chamber through the flow passage. Thus, the shock absorber can suppress vibration by generating a damping force resulting from the resistance of damping force generation means.
A shock absorber disclosed in JP1992-97133U includes a piston as a valve disc defining two chambers, a flow passage formed in the piston to allow communication between the two chambers, a window formed in the piston and connected to the flow passage, a valve seat formed on the piston and surrounding the outer periphery of the window, a plurality of leaf valves in the form of annular plates stacked on the piston, and an inner leaf valve and an outer leaf valve arranged substantially in the middle of these leaf valves. In the shock absorber disclosed in JP1992-97133U, the leaf valves, the inner leaf valve and the outer leaf valve serve as damping force generation means for applying resistance to working fluid passing in the flow passage.
Further, the outer leaf valve is arranged on the outer periphery of the inner leaf valve and formed to be thicker than the inner leaf valve. Thus, in the shock absorber disclosed in JP1992-97133U, a valve opening pressure of the leaf valves can be set high by applying initial deflection to the leaf valves stacked at an opposite piston side of the outer leaf valve and a large damping force can be generated when a piston speed is in a medium/high speed region.
When the piston speed is in the low-speed region, the working fluid passes through a known orifice formed by cuts provided on the leaf valves and a groove provided on the valve seat. Thus, the shock absorber can generate a damping force resulting from the resistance of the orifice.